textproduct: Rapid City

KEY MESSAGES

- Cooler temperatures are still in store through Thursday.

- Much needed rainfall through mid-week for some, but not all.

- Hot and dry conditions to return for the upcoming weekend.

DISCUSSION

(This Evening Through Tuesday) Issued at 113 PM MDT Tue Jul 21 2026

Latest water vapor imagery shows 500hpa ridge axis extending from Pacific NW southeast to the Gulf. Desert SW monsoonal moisture is streaming through NV/ID then into MT and the Dakotas. One weak wave is located in southwest MT/northwest WY with another more robust wave located in central NV. At the surface, Canadian high pressure is nosing into the Dakotas with northeast to easterly winds across our SD counties, and southeast winds across our WY counties. At 17Z, temperatures across the CWA vary from around 70F across the north, to the lower 80s across Campbell Co, WY and our southwestern SD counties.

Aforementioned wave located in southwest MT will slide into the CWA this evening/overnight while surface high pressure ridge drops southeast becoming mainly located along the I-29 corridor of the eastern Dakotas. Models continue to be bullish on pwat values, with amounts running 150-175% of normal by 06Z Wednesday. The probability of 1.50 or greater pwat values across much of the CWA ranges from 50-90%, and for 1.75 or greater ranges from 30-40% basically across our southern counties. The probability of seeing 0.25 of rainfall or greater from 06Z-12Z Wednesday is 40-50% and stretches in a corridor from KGCC-KRAP-KICR. Will continue with scattered to likely pops in the overnight period tonight for much of the area.

There will be a brief dry spell from Wednesday morning through early Wednesday evening as subsidence behind exiting wave clears things out. Pwat values still remain high, and by 00Z Thursday begin to push 200% of normal. Stronger wave currently located in central NV is expected to impact the area around this time as well, setting up the potential for some localized heavy rainfall to occur. Wouldnt be too terribly surprised Thursday morning to hear of some localized 1+ amounts of rainfall during the overnight hours.

Upper ridge then expands back into the mid-section of the country for the weekend, with 850hpa temps climbing back to around +36C by 00Z Sunday. Fridays highs may need to be trimmed down a skosh depending on how much rain falls Wednesday night/Thursday morning and the resultant dwpts. We might need to evaporate some of that moisture off before the mercury can really climb.

AVIATION

(For the 18Z TAFS Through 18Z Wednesday) Issued At 1206 PM MDT Tue Jul 21 2026

VFR conditions will prevail through 22/00z. After 22/00z, some showers/thunderstorms will move into the region. Localized MVFR/IFR conds may be possible in heavier rainfall. Have SHRA mentioned at both TAF sites tonight and overnight, but lower confidence if the sites will become MVFR/IFR.

UNR WATCHES/WARNINGS/ADVISORIES

SD...None. WY...None.